Transmission seems to be hunting, 2003 U320, need help

Topic: Transmission seems to be hunting, 2003 U320, need help (Read 1562 times) previous topic - next topic

Transmission seems to be hunting, 2003 U320, need help

September 17, 2014, 12:29:16 pm

Currently stopped at the West Gardiner plaza on the Maine turnpike and need assistance.

Transmission seems to be hunting, particularly on hills, mostly when gear selection is D/6. Not as much in D/5. Notice speedometer is a little "jerky" as well.

Fluid is fully warmed up and keypad shows level OK.

No codes on the Allison transmission keypad. No obvious codes on VMSpc history. No warning lights on dash. All parameters seem to be OK.

Calling James T. now but if anyone has an ideas. Thinking of looking for the output speed sensor as others have had that problem, but don't know what it looks like.

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #1 – September 17, 2014, 12:47:44 pm

Try this info on trouble shooting

http://www.rvtechlibrary.com/transmissions/3000_4000_operators.pdf

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #2 – September 17, 2014, 12:51:33 pm

I wish I could help. I can only suggest the computer is getting that same jerky speed reading you see, so is confused as to road speed and gear selection. Possibly whatever speed transducer Allison uses is having issues, or a bad connection.

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #3 – September 17, 2014, 01:10:18 pm

Thanks Dave - Steve's now checked all the connections on the transmission itself. None were loose but he did clean and CorrosionX each one and make sure it was properly reseated.

He's also checked the Allison ECM connections and all seemed to be tight.

Nothing looks loose or chewed on the engine.

We're about 45 minutes from the Allison shop in Portland and it's on our way to our next campground in Vermont. We're going to head towards them and see how it goes.

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #4 – September 17, 2014, 01:18:39 pm

At this point would zero in on the speed sensor on tail shaft, mag p/u, maybe loose or dirty with a chip on the magnet fluttering. Have seen that lil bummer.

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #5 – September 17, 2014, 01:54:21 pm

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #6 – September 17, 2014, 02:07:49 pm

No repeat of issues since connections were cleaned/cx'd. Thanks for that doc Dave. We are continuing to the campground and keeping our eye on things.

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #7 – September 17, 2014, 02:21:12 pm

Great news Michelle! Hope that did the trick.

Richard B

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #8 – September 17, 2014, 02:52:46 pm

Another thing you might want to check, is do you have a brake dragging? Or if you have a braking system on the toad, is that ok?

Ben Harris
1999 U320 40'

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #9 – September 17, 2014, 03:19:59 pm

Started back up

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #10 – September 17, 2014, 03:37:08 pm

Please keep us updated on the final diagnosis. This will be another good piece of information to add to our individual troubleshooting guides.

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #11 – September 17, 2014, 03:42:27 pm

If you can determine that it isn't the speed sensor here is some more things to look at.

Have Steve check the wires to the engine position sensor (cam sensor) It has 4 wires they are actually 2 pair. One set for the main sensor and one set for the backup. If the main fails it will go to the backup. If it is swapping back & forth it will cause a surge but it will be noticeable in all gears. If it completely quits it will leave you stranded as the ECM don't know when to fire the injectors. Pull the loom back & see if the wires are oil soaked and mush.

Have you checked to see if the throttle position sensor hasn't vibrated the screws loose. It could cause same problem but would most likely be noticed in all gears.

Pamela & Mike

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #12 – September 17, 2014, 03:48:07 pm

My road speed sensor was bad and it threw the check engine light. It will eventually derate the engine too.

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #13 – September 17, 2014, 04:20:40 pm

I have seen this when the cruise control is on going up hills and speeds and RPMs are right about where you might expect a downshift. It does then up then down. I just shut off the CC on hilly roads.

Hope it is n easy fix.

Roger

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #14 – September 17, 2014, 04:37:00 pm

You may have solved the problem with the cleaning & CorrosionX. How long were you set at the campground before this problem surfaced?

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #15 – September 17, 2014, 04:56:41 pm

The issue is definitely intermittent, and with there being no codes showing on the keypad, the Allison shop in NH felt it is most likely electrical and unique to FT. They didn't want to touch it. We are continuing to the campground and will check the wiring as suggested by Pamela and Mike. Will also check with Allison shop closer to campground tomorrow.

One thing I noticed this second episode was a brief series of tapping sounds with decreasing amplitude just before the downshift or torque converter dropping out of lockup from the general area of below our shower base. That's driver side rear wheel area.

Oh, and it's also thrown an abs light on the dash both times.

(Sorry for any typos, I'm posting from my phone)

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #16 – September 17, 2014, 05:27:27 pm

Michelle,
With this new info, slide under and see if you have lost one of your caliper slide pins. Not likely but possible. While under there check U joints & driveshaft slip joint for excess wear. A U joint going bad could shake the rear axle housing enough to set off an ABS alarm also.

P & M

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #17 – September 17, 2014, 05:33:08 pm

Definitely check everything in that general area under the coach. It could be one of any number of things, and the transmission issue could be only a symptom. Intermittent issues are always so much fun to diagnose!

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #18 – September 17, 2014, 07:33:21 pm

Quote from: D.J. Osborn – September 17, 2014, 05:33:08 pm

Intermittent issues are always so much fun to diagnose!

No kidding

After the second "act up" and stopping in Concord, NH at the Allison shop, no unusual hunting the rest of the drive into central Vermont, although the ABS light is still on (we'll pull its code tomorrow). We are safe at the campground and will start looking at everything tomorrow.

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #19 – September 17, 2014, 07:57:32 pm

It and you and Steve need a glass or two of vino and all will look much better!

Keep us posted!

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #20 – September 18, 2014, 03:05:29 pm

Quote from: Pamela & Mike – September 17, 2014, 03:42:27 pm

If you can determine that it isn't the speed sensor here is some more things to look at.

Output speed sensor externals are fairly greasy/oily, especially compared to other sensors. Steve had cleaned it yesterday and again today but we are thinking of going ahead and replacing that sensor.

Quote

Have Steve check the wires to the engine position sensor (cam sensor) It has 4 wires they are actually 2 pair. One set for the main sensor and one set for the backup.

Have you checked to see if the throttle position sensor hasn't vibrated the screws loose. It could cause same problem but would most likely be noticed in all gears.

P&M - where would these sensors be? Steve's ID'd the output speed, input/engine speed, what he believes is the retarder temperature, and turbine speed on the Allison, we don't know where the engine position sensor and throttle position sensor are.

All slide pins are present, nice and shiny with their helper springs attached. U-joints, etc., all seem fine.

ABS code was 3rd axle left, no response/signal and 3rd axle left, low current. Steve's inspected and cleaned the driver tag ABS sensor, it also was somewhat oily.

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #21 – September 18, 2014, 03:10:59 pm

Hey - just found this on the forum. Our ABS light didn't flutter, but wondering if it is the case than a wheel speed sensor could cause torque converter issue

Torque converter locking up and then unlocking at highway speeds.

Thoughts?

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #22 – September 18, 2014, 03:19:59 pm

That is a good find and possibly the problem. Another great advantage of the forum. If you can determine it is a bad wheel sensor they are relative cheep not even 1/10 of a coach buck.

Pamela & Mike

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #23 – September 18, 2014, 03:21:26 pm

Michelle, that sounds like you're on to something! I love this forum!

Re: Transmission seems to be hunting, 2003 U320, need help

Reply #24 – September 18, 2014, 04:20:00 pm

Quote from: Michelle – September 18, 2014, 03:05:29 pm

P&M - where would these sensors be? we don't know where the engine position sensor and throttle position sensor are.

Michelle,

The throttle sensor is easy to find & get to it. It is on the bottom of your throttle pedal and is held on with a couple of screws. If you lift the throttle petal and look on the right hand side you should see the 2 little screws.

The engine position sensor is located behind your air conditioner compressor & in front of your air compressor. Yes it is hid in a little hole. If you look down through the A/C compressor belt you can see the wire loom. The sensor is screwed it the block actually pointed toward the rear of the coach.
We were told by Cummins that the first generation of wire insulation that they used was sensitive to oil & would deteriorate over time the new ones have a different insulation to cure the problem.

Here is the best pic. I could get. The first is of the plug looking through the belts. The second is the sensor & plug.

Pamela & Mike

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